Waveguide tuner



Dec. 2, 1958 HQc. GlLcHRlsT ET AL 2,863,128

WAVEGUIDE TUNER Filed sept. 19, 195e y.. E f3- gl. 5

" JNVENTOR.

N WW@ WAVEGUIDE TUNER Harry C. Gilchrist, Pleasantville, and John F.Zaleski,

Valhalla, N. Y., assignors to General Precision Laboratory Incorporated,a corporation of New York Application September 19, 1956, Serial No.610,863

2 Claims. (Cl. S33-98) This invention relates to devices for matchingirnpedance discontinuities in waveguides.

Waveguides are widely used for the transmission of energy at microwavefrequencies and so long as the waveguide maintains the same dimensionsand contains no bends, junctions, loads, or the like, the energy can betransmitted without reflection. Practical circuits, of course, nearlyalways include one or more of such discontinuities which will causereection and power loss unless some provision is made for compensatingfor their presence.

One widely used technique for eliminating reflections caused by adiscontinuity is the use of a rod or screw inserted into the waveguideparallel to the lines of electric force. Such an arrangement introducesan additional reflection which can be made equal in amplitude butopposite in phase so as to cancel the reflection caused by thediscontinuity. If the screw is inserted through a longitudinal slot inthe face of the waveguide, the phase of the added rellection may beadjusted by varying the longitudinal position of the screw while themagnitude may be adjusted by varying the amount by which the screw isinserted. A number of tuners of this class have been constructed in thepast, but have been subject to the disadvantage that two adjustments arerequired to match a discontinuity. To overcome this disadvantage, theuse of a large asymmetrically placed screw having a projection on oneside beyond the end has been proposed. While this arrangement requiresbut a single adjustment, it is subject to the disadvantage that thevoltage standing wave ratio observed in tuning a mismatch is acomplicated function of the insertion.` This is because the reflectioncaused by the body of the screw remains fixed phase while that caused bythe projection varies, and also because the projection movestransversely as well as longitudinally.

It is an object of the present invention to provide a simple waveguidetuner for compensating for impedance discontinuities.

Another object is to provide a waveguide tuner having a single controlfor varying both the magnitude and phase of the susceptance.

Briefly stated, one embodiment of the invention comprises a thin rodinserted into the waveguide through a longitudinal slot on thecenterline. The amount of insertion is varied by rotating a cam whichbears on the end of the rod. As the cam rotates, it, together with therod, is moved longitudinally by the action of a lead screw.

For a clearer understanding of the invention reference may be made tothe following detailed description and the accompanying drawing inwhich:

Figure l is an isomeric view of a preferred embodiment of the invention;

Figure 2 is a fragmentary cross sectional view taken on the line 2-2 ofFigure l; and

Figure 3 is a cross sectional view taken on the line 3-3 of Figure l.

Referring first to Fig. 1, there is shown a rectangular States Patent()M 2,863,128 latented Dec. 2, 1958 waveguide section 11 supported by twoupstanding end pieces 12 and 13 which may also serve as flanges forconnecting the device to other microwave components. Mounted on top ofthe waveguide section 11, on one broad side thereof, is a block 14 ofrectangular cross section slightly narrower than the waveguide andextending the full length between the end pieces 12 and 13. Block 14 isfastened securely to the waveguide 11, as by soldering or brazing, so asto make the waveguide 11 and the block 14 effectively one piece. Anarrow slot 15 is cut through the block 14 and the waveguide 11 on thecenter line and at least one-half a guide wavelength long. A carriagecomprising two upstanding frame portions 16 and 17 with a bottom portion18 integral therewith is arranged to slide longitudinally along the topof the block 14 and the waveguide 11. Two plates 19 and 21 are fastenedto the carriage and help to guide it along the block 14 and waveguide11. A machine screw 22 is fastened at its ends to the end pieces 12 and13 and is positioned directly above the slot 15 and parallel thereto.

As best shown in Fig. 2, a sleeve 23 surrounds a portion of the screw 22and has corresponding threads on the inside thereof. One end of thissleeve 23 is fastened to an adjusting nut 24 so that rotation of the nutturns the sleeve and moves both the sleeve and the nut along the axis ofthe screw 22. The sleeve 225i passes completely through the frameportion 16 and part way through the frame portion 17 and rotates freelywithin these portions. A cam 25 is placed between the frame portions 16and 17 and is fastened to the sleeve 23 by means of a set screw 26 asshown in Fig. 3. lt can be seen that rotation of the nut 24 will causethe cam 25 to rotate and will also cause the entire assembly includingnut 24, the cam 25, the sleeve 23 and the entire carriage to movelongitudinally.

Referring now to Fig. 3, there is shown a conductive or nonconductiverod 27 which projects through the slot 15 in the block 14 and thewaveguide 11. The rod 27 makes a close fit in passing through a hole inthe bottom portion 18ct the carriage and the upper end of the rod isfastened to a plate 28. The plate 2S and with it the rod 27 are urgedupwardly by two springs 31 and 32 which bear against the bottom of theplate and are seated in holes passing through the bottom portion 18 ofthe carriage and the two plates 19 and 21. The cam 25 bears against theupper portion of the plate 28 holding it in position against the urgingof the springs 31 and 32. It can be seen that rotation of the cam 25will adjust the amount by which the rod 27 is inserted into the interiorof the waveguide 11 and the dimensions are selected so that thisinsertion varies from zero to onequarter of a wavelength.

Since the slot 15 is located on the centered line of one broad face ofthe guide 11 and since the guide is normally used to propagate thedominant TEM, mode very little powerwill escape through the slot. Poweris prevented from leaking through the slot in the vicinity of the rod bymaking the distance from the inner wall of the waveguide to the top ofthe block 14 equal to one-quarter of a guide wave length and by a chokecomprising an annular recess 33, one-quarter of a guide wavelength long,formed inV the bottom portion 18 of the carriage.

The apparatus is used to compensate for a discontinuity in a waveguidetransmission band by inserting the device into the path by means of theend pieces 11 and 13. The nut 24 is turned until the best voltagestanding wave ratio is obserbed. Rotation of the nut 24 rotates the cam25 thereby adjusting the amount of the insertion of the rod 27. Sincethe insertion can be` varied from zero to a quarter of a wavelengthreflections of any magnitude can be compensated for within one-half arevolution of the nut 24. The phase of the reflection may be adjusted bycontinued rotation of the nut 24 to place the rod 27 at any longitudinalpoint within a half guide wavelength. Thus, the entire adjustment forboth magnitudeV and phase is accomplished with but a single control. Ofcourse, not every magnitude of insertion of ythe rod 27 can be securedcontinuously within this haltv wavelength distance but only at manydistances separated by one-half the pitch -of the screw 22. By using ascrew with a line thread this limitation is minimized and as a practicalmatter is not important.

A speciic embodiment has been described for illustrative purposes onlyand many modifications will occur to those skilled in the art. It istherefore desired that the invention be limited only by vthe true scopeof the appended claims.

What is claimed is:

l. A tuner comprising a section of waveguide having a longitudinal slotin the wall, a carriage slidable along the outer wall, a conductive rodmounted on said carriage in alignment with said slot, a cam -mounted onsaid carriage and cooperating with said rod for varying the amount bywhich said rod projects through said slot into the interior of saidwaveguide, and screw and nut means for simultaneously actuating said camand sliding said carriage along said waveguide.

2. A waveguide tuner comprising a section of a rectangular waveguidehaving a slot along the center line of one broad side, a carriage onsaid broad side and slidable lengthwise of said waveguide section, aconductive rod mounted on said carriage in alignment with said slot,spring means on said carriage urging said rod away from said waveguidesection7 a lead screw mounted above said broad face and parallel to theaxis of said waveguide section, a cam freely rotatable about said leadscrew and mounted between two upstanding frame portions of said carriagefor inserting said rod into said waveguide against the urging of saidspring, a sleeve threaded onto said lead screw and connected to said camand an adjusting nut secured to said sleeve, whereby rotation of saidnut rotates said cam, adjusts the insertion of said rod and slides saidcarriage along said waveguide.

References `Cited in the tile of this patent UNI-TED STATES PATENTS2,496,837 Woodyard Feb. 7, 1950 ,2,578,249 Johnson Dec. l1, 19512,705,307 Nyswander Mar. 29, 1955

